With the spread of information terminals, there are increasing demands for a flat panel display that serves as a display for a computer. Further, with development of the information technology, there has been increased a chance for information offered in a form of a sheet of paper medium in the past to be offered in an electronic form. An electronic paper or a digital paper is demanded increasingly as a display medium for a mobile that is thin, lightweight and handy.
In the case of a display device of a flat sheet type, a display medium is generally formed using an element that employs a liquid crystal, organic EL or electrophoresis method. In the display medium of this kind, a technology for using an active driving element comprised of a thin-film transistor (TFT), serving as an image driving element, is the main current for ensuring uniform image brightness and an image rewriting speed.
The TFT is commonly manufactured by a process comprising forming, on a glass substrate, a semiconductor layer of a-Si (amorphous silicon) or p-Si (poly-silicon) and metal films of source, drain and gate electrodes, in order. In the manufacture of a flat panel display employing such a TFT, a photolithography step with high precision is required in addition to a thin layer forming step requiring a vacuum line carrying out a CVD method or a sputtering method or a high temperature treatment step, which results in great increase of manufacturing cost or running cost. Recent demand for a large-sized display panel further increases those costs described above.
In order to overcome the above-described defects, an organic thin-film transistor employing an organic semiconductor material has been extensively studied (Refer to Patent Document 1).
Various studies have been made to increase carrier mobility. Disclosed, for example, is a technique in which carrier mobility is increased when a silicon oxide layer is used as a gate insulating layer and its surface is subjected to treatment employing a silane coupling agent.
[Refer to “Advanced Material”, 2002, No. 2, p. 99 (review)]
Disclosed also is a technique in which carrier mobility is increased by forming a film composed of a fluorine-containing polymer provided on a gate insulating layer. (Refer to Patent Document 2)